 /*******************************************************************************
  * Copyright (c) 2000, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.core.internal.expressions;

 import org.w3c.dom.Element ;

 import org.eclipse.core.runtime.Assert;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IConfigurationElement;

 import org.eclipse.core.expressions.EvaluationResult;
 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.ExpressionInfo;
 import org.eclipse.core.expressions.IEvaluationContext;

 public class EqualsExpression extends Expression {
     /**
      * The seed for the hash code for all equals expressions.
      */
     private static final int HASH_INITIAL= EqualsExpression.class.getName().hashCode();

     private Object fExpectedValue;
     
     public EqualsExpression(Object expectedValue) {
         Assert.isNotNull(expectedValue);
         fExpectedValue= expectedValue;
     }
     
     public EqualsExpression(IConfigurationElement element) throws CoreException {
         String value= element.getAttribute(ATT_VALUE);
         Expressions.checkAttribute(ATT_VALUE, value);
         fExpectedValue= Expressions.convertArgument(value);
     }

     public EqualsExpression(Element element) throws CoreException {
         String value= element.getAttribute(ATT_VALUE);
         Expressions.checkAttribute(ATT_VALUE, value.length() > 0 ? value : null);
         fExpectedValue= Expressions.convertArgument(value);
     }

     public EvaluationResult evaluate(IEvaluationContext context) throws CoreException {
         Object element= context.getDefaultVariable();
         return EvaluationResult.valueOf(element.equals(fExpectedValue));
     }

     public void collectExpressionInfo(ExpressionInfo info) {
         info.markDefaultVariableAccessed();
     }

     public boolean equals(final Object object) {
         if (!(object instanceof EqualsExpression))
             return false;
         
         final EqualsExpression that= (EqualsExpression)object;
         return this.fExpectedValue.equals(that.fExpectedValue);
     }

     protected int computeHashCode() {
         return HASH_INITIAL * HASH_FACTOR + fExpectedValue.hashCode();
     }
 }

